多选题

用C++编写的函数中，下面哪个swap函数在调用后可以正确交换输入参数的值:void swap1( ); void swap2( ); void swap3( ); void swap4( ); void main( ){ int a=1; int b=2; swap1(a,b); printf("a=%d b=%d \n", a, b); int c=1; int d=2; swap2(&c, &d); printf("c=%d d=%d \n", c, d); int e=1; int f=2; swap3(e, f); printf("e=%d f=%d \n", e, f); int g=1; int h=2; int *gp = int *gh = swap4(&gp, &gh); printf("e=%d f=%d \n", *gp, *gh); } void swap1(int a, int b){ int tmp=a; a = b; b = tmp; } void swap2(int* a, int* b){ int tmp=*a; *a = *b; *b = tmp; } void swap3(int& a, int& b){ int tmp=a; a = b; b = tmp; } void swap4(int **p1, int **p2){ int *tmp = *p1; *p1 = *p2; *p2 = tmp; }

Question

A. swap1

B. swap2

C. swap3

D. swap4